1. Field of the Invention
This invention relates to a magnetic disk pack containing a magnetic disk having a recording medium coated on one or both of its surfaces so that picture information can be magnetically recorded with a high recording density and the recorded picture information can then be reproduced for observation by the viewer, and relates also to a magnetic disk recording/reproducing apparatus suitable for recording and reproduction of picture information on and from such a magnetic disk.
2. Description of the Related Art
An electronic still camera system has been developed and is now in practical use. This electronic still camera system comprises the combination of an imaging device such as a solid-state imaging unit or a camera tube and a recording device using a recording unit in the form of a rotatable magnetic disk which is inexpensive and has a relatively large memory capacity. A still picture of a subject is taken by the imaging device, and the still picture information is recorded on the magnetic disk in the recording device to be then reproduced or printed by means such as a television system or a printer. The magnetic disk used in the electronic still camera system is formed by coating a magnetic material on one or both surfaces of a thin disk-shaped base of a synthetic resin. Therefore, the magnetic disk is flexible but susceptible to a mechanical force tending to cause deformation. Also, because attachment of dust or like foreign matter on the surface of the magnetic disk adversely affects the accuracy of picture information recording and reproduction, the magnetic disk is commonly sold in the form of a magnetic disk pack in which the magnetic disk is housed in a deformation-resistive protective casing.
FIG. 12 is a partly cut-away perspective view of the front surface side of such a magnetic disk pack, and FIG. 13 is a sectional view taken along the line XIII--XIII in FIG. 12. As shown in FIGS. 12 and 13, the magnetic disk pack generally designated by the reference numeral 11 is principally formed of a protective casing 14 consisting of an upper case 12 and a lower case 13 made of a synthetic resin, a flexible magnetic disk 15 rotatably housed within the protective casing 14, and a shutter 16 slidably mounted along one of the marginal end edges of the upper surface of the protective casing 14. This shutter 16 is made of a metal such stainless steel and has a generally U-like sectional shape. A center core 17 acting as a reinforcing member is provided at the center of the magnetic disk 15. A shaft-receiving hole 18 is bored in the center core 17 so that a drive shaft of a recording/reproducing apparatus can be inserted into this hole. The upper and lower surfaces of the center core 17 are exposed to the outside from aligned central openings 19 of the upper and lower cases 12 and 13 respectively. The upper case 12 is formed with a window 20 into which a regulation member 22 of the recording/reproducing apparatus is inserted, and the lower case 13 is formed, at a position corresponding to the window 20, with a window 21 into which a magnetic head 23 is inserted, as shown in FIG. 13. These windows 20 and 21 are opened and closed by the sliding movement of the shutter 16.
The size, dimensional accuracy, etc. of the magnetic disk pack having such a structure are now standardized, and the magnetic disk pack enjoys compatibility in any of the magnetic disk recording/reproducing apparatuses made by various makers.
However, the magnetic disk recording/reproducing apparatus themselves are not standardized yet and have a variety of structures and designs different depending on the maker. Thus, the shape and size of the regulation member 22 can be freely designed.
JP-A-61-9868 (1986) proposes a magnetic disk pack in which, in lieu of the regulation member 22, a negative pressure is utilized to attain desired head touch. (Herein, the term "head touch" is used to indicate attainment of satisfactory recording or reproducing contact between a magnetic head and a magnetic disk.) That is, JP-A-61-9868 discloses an arrangement as shown in FIG. 14A. Referring to FIG. 14A, two tapered control members 26 and 25 are disposed on the upstream and downstream sides respectively of a magnetic head 24 so that a negative pressure can be induced between a rotating magnetic disk 27 and the control members 25,26. (Herein, the terms "upstream" and "downstream" are used to indicate the positions of the control members 25 and 26 relative to the direction of rotation of the magnetic disk 27 shown by the arrow.) When the negative pressure is induced, the magnetic disk 27 is attracted toward the control members 25 and 26 so that the magnetic head 24 can achieve stable recording or reproducting contact with the magnetic disk 27.
Thus, in the prior art apparatus, the desired head touch between the magnetic head 23 or 24 and the magnetic disk 15 or 27 is ensured by means such as the regulation member 22 or control members 25 and 26. Therefore, ensurance of good head touch is determined by the selection or design of the means described above, and this fact adversely affects the compatibility of the magnetic disk pack. Further, attempts at high-band recording are now made in the field of magnetic recording by electronic still cameras and, in such a case, ensurance of better head touch is demanded.
On the other hand, there is an increasing demand for recording picture information on both surfaces of a magnetic disk housed within a magnetic disk pack. However, in view of various differences between the magnetic disk pack and a 3.5-inch or 5.25- inch floppy disk, the known technique of information recording on both surfaces of the floppy disk can not be applied to the magnetic disk pack. That is, as shown in Table 1, the thickness and diameter of the recording medium in the case of the magnetic disk pack are smaller than those of the 3.5-inch or 5.25-inch floppy disk, although the rotational speed of the magnetic disk is higher than that of the floppy disk. Further, a magnetic head makes sliding contact with a smaller area of each surface of the magnetic disk than that of the floppy disk as also shown in Table 1. This means that, because the flexibility of the magnetic disk used in the magnetic disk pack is far higher than that of the floppy disk, the magnetic heads cannot achieve stable sliding contact with the front and back surfaces of the magnetic disk when the magnetic heads are merely pressed onto those surfaces.
TABLE 1 ______________________________________ Article Magnetic Floppy Particulars disk pack disk ______________________________________ Thickness of 40 .+-. 2 .mu.m* 80 .mu.m recording medium Diameter of 47 mm* 3.5 inches, 5.25 inches recording medium Recording surface One* Two Surface coated with Two Two magnetic material Head sliding &gt;300 .mu.m.sup.2 Several mm.sup.2 contact area ______________________________________ *According to the present standards.
In the case of the floppy disk adapted for information recording on its front and back surfaces, magnetic heads are always brought into contact with the both surfaces of the recording medium at the same positions by means of gimbal springs. However, when this method is applied to the magnetic disk pack, the magnetic disk tends to be subjected to wear and damage due to application of an excessively high pressure per unit area, because the area with which the magnetic head makes sliding contact is quite smaller than that of the floppy disk.
FIG. 1 of JP-A-62-1168 (1987) shows a magnetic disk recording/reproducing apparatus as shown in FIG. 15. Referring to FIG. 15, a pair of magnetic heads 222 and 223 are disposed opposite to each other on both sides of a rotatable magnetic disk 221 in slightly spaced apart relation, and a pad 224 or 225 is pressed onto the front or back surface of the magnetic disk 221 so as to successively bring the front or back surface of the magnetic disk 221 into contact with the magnetic head 222 or 223.
However, such an apparatus is defective in that a complex mechanism is required for moving the pads 224 and 225, and the magnetic disk 221 tends to be subjected to wear due to the continuous sliding contact of the pad 224 or 225 with the magnetic disk 221.